Generally, a far-field measurement method, a near-field measurement method, a Fresnel Zone measurement method and the like may be enumerated as methods for measuring the radiation property of an antenna.
Among these, the far-field measurement method has an advantage of obtaining a desired value by one injection, but has a disadvantage that the size of a chamber needs to be large because keeping a distance between a sources antenna and a test antenna as much as far-field condition is required.
The distance satisfying the far-field condition is R=2*D2/λ, and D is the diameter of an antenna aperture, λ is the wavelength of a measurement frequency. For example, a gap filler antenna having a size 2 meter and a frequency of 0.8 GHz needs to secure distance of more than 22 meters from the source antenna. Therefore, a large chamber having a size of more than 30 m is necessary, considering size of an absorber and location of a positioner and the like.
The near-field measurement method may be applied within a small chamber because it is performed at a distance closer than that of the far-field measurement method. However, it takes a long time to obtain all the data because it is necessary to obtain the value of power at an interval smaller than a half-wavelength. Further, it takes a long time to convert near-field to far-field.
The Fresnel Zone measurement method may be performed within a small chamber having a size equal to or smaller than ⅕ times of far field chamber because it is performed in a middle distance of those of the far field measurement method and near field measurement method. In terms of a size of the antenna to be measured, a maximum size of the antenna which can be far-field chamber may be increased to two time or more of that of the existing antenna is compared. Further, in terms of time for obtaining and converting data, the equal to or more than one several times time may be shortened in comparison with the existing near-field measurement method.
The Fresnel Zone measurement method according to the prior art, may be classified into alpha angle change method, height change method, and phi angle change method depending on a scanning method. The alpha angle change method needs a positioner and a turntable capable of changing an altitude angle because scan is performed while changing an altitude angle between a plane of a source antenna and that of a test antenna. The height change method needs a height adjustable positioner and a turntable because the scan is performed while changing the height of the source antenna or the test antenna. The phi angle change method needs two positioners and a turntable because the scan is performed while changing the phi angle between the source antenna and the test antenna. Because the far-field chamber has two positioners and a turntable, the phi angle change method may be easily applied thereto.
However, a high-gain antenna typically weighs much so that the torque of the motor needs to be significantly large in order for rotating a roll angle of the test antenna to 360 degrees. Further, a linear antenna such as a gap filler antenna has a large amount of rear radiation so that it is much influenced by the roll positioned. Therefore, it is difficult to calculate accurate gain and patterns.